Some pastes contain a substitute for eugenol e.g. a carboxylic acid.
The 2 pastes come in contrasting colours and are dispensed in a 1:1 ratio. They
are mixed to give a paste of even colour. The setting reaction is shown below:

ZINC
OXIDE (excess)

ZINC
OXIDE (UNREACTED)

+

®

+

EUGENOL

EUGENOL

The set material contains both some unreacted zinc oxide and eugenol.
Any movement of the tray as the paste is hardening will lead to a deformed,
inaccurate impression. Setting time depends on: